1. Field of the Invention
The present invention relates to a hard disk drive with a recording head, and more particularly to a head amplifier circuit suitable for eliminating the residual magnetism of a recording head, and a hard disk drive with the head amplifier circuit.
2. Description of the Related Art
In hard disk drives, data is written to a disk medium by supplying their recording heads with write currents (recording currents) corresponding to write data. When a write current is supplied to a recording head, a recording magnetic field occurs at the head. This magnetic field permits magnetic recording (write operation) corresponding to write data to be performed on a disk medium.
The supply of the recording current to the recording head is stopped after a write operation is performed. At this time, it is known that a magnetic domain may well remain at the recording head, i.e., the recording head may be magnetized. When data is recorded on one or several data sectors of a magnetic disk medium by the recording head, and then the above phenomenon has occurred, all or part of the data or servo data recorded on the data sector and sectors subsequent to the data sector may be erased.
To avoid this, techniques for eliminating the residual magnetism of a recording head have been proposed. For instance, Jpn. Pat. Appln. KOKAI Publication No. 2-64903 (document 1) describes a technique for supplying a recording head with a recording current of a constant frequency as a degaussing current immediately after a write operation of the recording head. The supply of the degaussing current prevents the recording head from remaining magnetized. The time immediately after a write operation specifically means the time immediately after the write gate (write gate signal) is turned off. The recording current of a constant frequency (degaussing current) is generated based on dummy write data. The degaussing current is characterized in that its amplitude gradually attenuates.
Further, Jpn. Pat. Appln. KOKAI Publication No. 4-228103 (document 2) describes a technique for monotonically decreasing a recording current, supplied to a recording head, for a preset period (characteristic relaxation period) immediately after the write gate is turned off. In this case, the recording current is attenuated along a preset inclination or decay index curve, thereby preventing the recording head from remaining magnetized. Namely, document 2 describes a technique for preventing a recording head from being kept magnetized. Document 2 also describes supply, for the preset period, of a recording current of a higher frequency than in a data write operation. This high-frequency recording current is attenuated so that the envelop curve of the amplitude is monotonically decreased.
The techniques (hereinafter referred to as prior art) described in documents 1 and 2 both aim to eliminate the residual magnetism of the recording head by recording read-unnecessary data as the rear end of predetermined write data while gradually attenuating the recording current. In particular, document 1 discloses (1) frequency, (2) period for attenuation and (3) attenuation configuration used as parameters for attenuating the recording current. Attenuation of the recording current using optimal parameters may reliably eliminate the residual magnetism of the recording head.
However, it has become clear that the prior art cannot completely eliminate the residual magnetism of recent magnetic heads for high-density recording. Moreover, the time required to attenuate the recording current is about ten to several hundred nanoseconds. In the prior art, unnecessary data is recorded on an area of the magnetic disk medium corresponding to this time. By the unnecessary data, the formatting efficiency of the magnetic disk medium is reduced.